<!doctype html>
<!--
 * Copyright 2020 The Chromium Authors. All rights reserved.  Use of this
 * source code is governed by a BSD-style license that can be found in the
 * LICENSE file.
-->
<html>
<head>
  <title>A guest that echoes postMessages.</title>
  <script>
    window.addEventListener('message', (e) => {
      e.source.postMessage(e.data, e.origin);
    });
  </script>
</head>
</html>
